将null分配给javascript var-最终为String [英] Assign null to javascript var - ends up as String

问题描述

我已将变量初始化为以下内容:

I have initialized my variable as the following:

var name = null;

如果我检查像这样的值，它不会执行任何操作:

If I check it's value like this it doesnt do anything:

if(name == null) {
    alert("Name = null");
}

但是，如果我将if子句更改为该子句，它将起作用:

But if I change the if-clause to that, it works:

if(name == "null") {
    alert("Name = null");
}

为每一个帮助感到高兴.

Happy for every help.

推荐答案

您可能正在全局范围内运行它，在这种情况下， name 指的是

It's likely that you're running this is in global scope, in which case name refers to the Window.name property. Assigning a value to this property automatically causes the value to be converted to a string, for example, try opening up your browser's console and typing this:

var name = 123;
alert(typeof name); 

您很可能会收到一条警报，提示您读取 string .

You'll most likely get an alert that reads string.

但是，如果将其放置在 IIFE 中(并确保您拥有 var 声明)，其行为符合预期:

However, if you place this in an IIFE (and ensure that you have a var declaration), it behaves as expected:

(function() {
    var name = null;
    if(name == null) {
        alert("Name = null"); // shows alert
    }
})();

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